1. Field of the Invention
The present invention relates to a component mounting method and device which are used in a component mounting apparatus for mounting an electronic component on an electrode in a process of mounting operation in which a paste of cream solder is applied on an electrode on a circuit board, on which an electronic component which is positioned above the electrode is mounted, after which the cream solder is heated and melted to join the component onto the electrode.
2. Description of the Related Art
FIG. 4 is a plan view typically showing a primary structure of a component mounting device, in which a plurality of parts cassettes 42 in a component feeding unit 43, respectively accommodating different types of electronic components, are moved to a position where the component is picked up by a suction nozzle unit 41 in the order of mounting onto the circuit substrate 44.
The suction nozzle unit 41 has a rotary structure, which is constructed such that a plurality of suction nozzles 40 mounted thereon are successively moved on a circular track for picking up an electronic component from the parts cassette 42 in the component feeding unit 43 and mounting it onto the circuit substrate 44 which has been loaded to a mounting position. The suction nozzle unit 41 rotates to successively transfer each of the suction nozzles 40 from the positions denoted at encircled numerals 1 to 10 in a clockwise direction as shown in the figure. The electronic component is picked up from the parts cassette 42 at a component pick-up position (component pick-up point) denoted at encircled numeral 5, the picked-up posture of the component is recognized with image recognition process using a camera at a posture recognizing position (component recognizing point) denoted at encircled numeral 7, and the posture of the component is corrected around the axis of the suction nozzle 40 by its rotation based on the recognition results of the picked-up posture of the component at a posture correcting position (component position adjusting point) denoted at encircled numeral 9.
Meanwhile, the circuit substrate 44 is supported on an X-Y table (not shown) for free movements in X- and Y-directions, so as to bring a predetermined position of the circuit substrate 44 on which an electronic component is to be mounted is brought under a component mounting position (component mounting point) denoted at encircled numeral 10 of the suction nozzle unit 41. The circuit substrate 44 is also moved in directions for correcting displacement of the component in X- and Y-directions based on the picked-up posture recognition results. It is thus possible to mount an electronic component 45 picked up by the suction nozzle 40 which is displaced as shown in FIG. 5 precisely on the predetermined position on the circuit substrate 44.
However, in high density chip mounting of recent years, the space between two adjacent components have become smaller and smaller. As a result, especially in the case where the outer dimensions of the component are smaller than those of the suction nozzle, and under a condition that the center of the suction nozzle and that of the component are not in register with each other, it is often the case that the suction nozzle and an electronic component which has previously mounted on the circuit board interfere with each other, thus causing mounting errors. As shown in FIG. 6, for example, when mounting the electronic component 45 picked up by the suction nozzle 40 next to the electronic component 46 which has already been mounted on the circuit substrate 44, if the electronic component 45 held with the suction nozzle 40 is displaced from a prescribed position of the nozzle, the suction nozzle 40 which is lowered so as to mount the electronic component 45 to a predetermined position will hit the electronic component 46 previously mounted, which may cause the component 46 to be tilted or sprung out.
Also, the electronic component mounting device has an automatic recovery function in the case of failing to mount a component due to errors in picking up action, which is implemented such that the component which the nozzle failed to mount is mounted after all the other components have been mounted. In such a case, since the mounting order is different from the normal one, the component has to be mounted between the other components which have already been mounted, wherefore if the position of the component held by the suction nozzle is displaced, it is more often the case that the suction nozzle and the previously mounted component interfere with each other, causing frequent errors in mounting operation of the components onto the circuit substrate 44. In particular, it may cause a serious problem if the height of the component which has already been mounted is larger than that of the component which is going to be mounted later.